1. Field of the Invention
The invention relates to antennas, and in particular to patch antennas.
2. Background Information
Patch antennas are very popular because they are simple and cheap to fabricate, easy to modify and customize for a variety of applications, and are light weight and have a low profile so are easily concealed on or within a device. A simple patch antenna comprises a planar metal antenna plate (patch) suspended above a larger ground plane. Typically the patch is a half-wavelength long. The antenna signal is carried on a feed wire attached to the patch along one edge. A simple patch antenna of this type can be fabricated on a dielectric substrate employing similar lithographic printing techniques as those used to fabricate printed circuit boards. Despite their numerous benefits and wide use, patch antennas have a number of drawbacks including narrow bandwidth, low efficiency and low power handling capability.
The huge growth of wireless communications has necessitated the development of bandwidth boosting techniques over recent years. With the widespread exploitation of thick substrate, various bandwidth enhancement techniques, such as U-slotted patch
[Lee, K. F., Luk, K. M., Tong, K. F, Shum, S., Huyunh, M. T., and Lee, R. Q.: ‘Experimental and simulation studies of coaxially fed U-slot rectangular patch antenna’. IEE Proc., Microw. Antennas Propag., 1997, 144, (5), pp. 354-358], capacitive feed [Vandenbosch, G. A. E., and Capelle, A. R. V: ‘Study of the capacitively fed microstrip antenna element’, IEEE Trans. Antennas Propag., 1994, AP-42, (12), pp. 1648-1652], and L-shaped probe feed [Mak, C. L., Luk, K. M., Lee, K. F., and Chow, Y. L.: ‘Experimental study of a microstrip patch antenna with an L-shaped probe’, IEEE Trans. Antennas Propag., 2000, AP-48, (5), pp. 777-783], have been proposed which achieve substantial increases in impedance bandwidths of more than 30%, but suffer from various problems including high-cross polarization, inconsistent gain and unstable radiation patterns. A differential feed L-probe patch antenna has been proposed [Ref: X. Y. Zhang, Q. Xue, B. J. Hu, and S. L. Xie, “A wideband antenna with dual printed L-probes for cross-polarization suppression,” IEEE Antennas and Wireless Propagation Letters, vol. 5, pp. 388-390, February 2006] that can achieve 45% bandwidth impedance and low cross polarization. The impedance bandwidth of the differential feed L-probe patch antenna is wide enough to serve various wireless communications systems. However, there exists a need for a wider impedance bandwidth.
Accordingly, it is an object of the present invention to provide a patch antenna which overcomes or at least ameliorates at least one or more of the problems with known patch antennas. It is a further object of the present invention to provide a patch antenna which is suitable, or at least more suitable than known patch antennas, for use in a various wireless communications device and differential-fed antennas.